1. Field of the Invention
The invention relates to a supercharged device for internal combustion engines, and more particularly to a compressor unit used for a turbocharger.
2. Description of the Related Art
In recent years, with the substantial increase of the engine power, the compression ratio of the turbocharger is rising. But under the constraints of the turbocharger structure, a number of new industries problems are encountered at the supercharger efficiency of the turbocharger compressor. Under the condition of the high compression ratio, the flow friction losses at the side of the turbocharger and the gap loss during rotation of the compressor blades have more and more restricted the increase of the turbocharger efficiency. With the rising speed of the turbocharger, the relative inlet speed and angle of the leading edge of the compressor impeller are increasing, which constrains the air flow of the turbocharger, and the matching of the supercharger and the engine is more difficult.
As shown in FIG. 1, the compressor section of a turbocharger includes three parts: a compressor housing 1, a compressor impeller 4, and a gas diffuser channel 5. During normal operation, with the drive of a turbine shaft 12, the compressor impeller 4 is high-speed rotating to compress centrifugally the clean air inhaled from an air inlet 2. When the high-speed compressed gas enters into the gas diffuser channel 5 from the exit of the compressor impeller, the kinetic energy begins to transform into the pressure energy. While the gas enters an air collection channel 3 of the compressor housing under the constraint of the gas diffuser channel 5, and then enters the engine combustion chamber for combustion through the piping connected to the outlet side of the compressor housing 1. When the pressurized air flows in the gas diffuser channel 5, a diffuser channel wall 51 and a connection plate diffuser wall 11 perform the radial constraint of the air, during which the friction is produced and reduces the compressor efficiency.
To meet the acceleration and response requirements of engines, the turbochargers need the rotation speed of tens of thousands per minute, hundreds of thousands per minute or even higher. Limited by the structure and layout of the turbocharger compressor, a gap a1 must be retained between an outer contour surface 41 of the compressor impeller 4 and an inner contour surface of the compressor housing 1, to ensure no friction between them and to avoid turbocharger failure under the high-speed rotation of the compressor impeller 4. To ensure reliable operation, the gap a1 is generally about 0.4-0.8 mm, which is about 4%-8% of the height of the inlet leading edge 9 of the impeller. The gas inhaled from the inlet leading edge 9 of the impeller into the compressor impeller 4 is centrifugally compressed and flows along the hub contour of the impeller and the inner contour surface of the compressor housing 1. During the compression process, the gas turbulence in the gap a1 between the inner contour surface of the compressor housing 1 and the outer contour surface 41 leads to the rapid decline of the compressor efficiency. Therefore, the gap a1 should be as small as possible, up to the zero-clearance state for the high-efficient compression.
To increase the compressor flow, a compressor structure with dual inlet channels is used on the turbocharger. As shown in FIG. 2, there are an air inlet 2 and an inlet 14 of a compressor outflow channel at the inlet end of the compressor housing 1. One end of the inlet 14 of the compressor outflow channel is connected to a supplement air intake groove 13. When the compressor impeller 4 is high-speed rotating driven by the turbine shaft 12, and the intake of the air from the impeller inlet leading edge 9 is restricted, part of air enters from the supplement air intake groove 13 to increase the flow. In the low-speed condition, it has played a certain role to restrain the turbocharger surge. But the compressor structure with dual-channels is a simple intake regulation device, with a limit for the improvement degree, and the presence of the supplement air intake groove 13 has created an additional space losses and an aerodynamic noise.
Thus, an advanced compressor device is required to solve the problem of the turbocharger efficiency, to solve the scratching shell failure after the turbocharger is worn, and to extend the turbocharger life, as well as to further increase the compressor flow and the pressure ratio.